Integrated circuits frequently have several types of metal oxide semiconductor (MOS) transistors, each type having certain electrical properties. For example, an integrated circuit may have logic transistors which perform binary arithmetic and/or Boolean logic functions at high speed, input/output (I/O) transistors which commonly operate at higher voltages than the logic transistors and interface with signals transmitted to and from the integrated circuit, transistors in analog circuits, and drain extended transistors, which may interface with power supplies such as batteries connected to the integrated circuit. MOS transistors are fabricated using ion implantation processes to form n-type and p-type ion implanted regions in the MOS transistors, having halo regions, lightly doped drain (LDD) regions or medium doped drain (MDD) regions, and source/drain (S/D) regions. Details of spatial configurations of ion implanted regions, such as lateral extents of overlap or separation between the ion implanted regions and gates of the MOS transistors, affect the electrical properties of the MOS transistors. Other physical properties of the ion implanted regions, having doping densities and dopant species, also affect the electrical properties of the MOS transistors. MOS transistors designed to have different electrical properties frequently have different spatial configurations of ion implanted regions, and may also have different doping densities and different distributions of dopant species.
Ion implanted regions are typically formed using photoresist patterns which expose areas on integrated circuits to be implanted. The photoresist patterns are removed during subsequent processing. Forming and removing photoresist patterns undesirably increases fabrication cost and complexity of integrated circuits.